With the recent developments in digital technologies, size reduction, performance enhancement, and multifunctionalization of various electronic devices have been advanced. Many of these electronic devices use semiconductor devices (LSI: Large Scale Integration) having built-in storage elements. The storage elements include volatile memory which loses data when power supply stops, and non-volatile memory which can retain data without power supply.
The volatile memory includes DRAM (Dynamic Random-Access Memory), SRAM (Static Random Access Memory), and the like, and has an advantage of allowing high-speed data access. Meanwhile, the non-volatile memory includes EEPROM (Electrically Erasable Programmable Read Only Memory), flash memory, FeRAM (Ferroelectric Random Access Memory), and the like. The above-described semiconductor devices are provided with either or both of the volatile memory and the non-volatile memory, depending on the purposes of use of the semiconductor devices.
FeRAM, which is a kind of non-volatile memory, has advantages of allowing fast-speed data access, consuming low power, and allowing high-frequency rewriting. FeRAM uses ferroelectric capacitors to store data. The ferroelectric capacitors each have a structure in which a film made of a ferroelectric material having a ferroelectric characteristic (spontaneous polarization), such as PZT (PbZrxTi1-xO3, provided that 0<x<1), is sandwiched between a pair of electrodes.    [Patent Document 1] International Patent Pamphlet No. WO 2004053991    [Patent Document 2] Japanese Laid-open Patent Publication No. 2008-071825    [Patent Document 3] Japanese Laid-open Patent Publication No. 2006-318941
Semiconductor devices are preferably more miniaturized and more power-saving. To meet these demands, FeRAM preferably has a ferroelectric film having a reduced film thickness.